PROJECT SUMMARY/ABSTRACT While air quality has improved over the past decades, air pollution is ubiquitous and the absolute number of people affected is a major public health concern. In 2013, the International Agency for Research on Cancer classified outdoor air pollution and particulate matter (PM) as carcinogenic to humans and a cause of lung cancer. This recent classification calls for prompt action to address the gaps in the epidemiologic literature on the role of air pollution in increasing the risks for lung cancer and chronic obstructive pulmonary disease (COPD), two of the top four causes of death in the United States. Thus, we designed the following aims, leveraging the rich environmental, lifestyle, neighborhood, molecular, and surveillance data of the long- standing Multiethnic Cohort (MEC) Study. We propose in Aim 1 to quantify and characterize the associations between estimated exposure to airborne particulate matter (PM2.5, PM10) and lung cancer risk among 112,023 California (CA) MEC participants with 3,057 lung cancer cases. In Aim 2 we will quantify and characterize the associations between PM2.5, PM10, and risk of COPD among 46,000 CA MEC participants with Medicare data, including 11,508 COPD cases. In Aim 3 we will investigate the relationships between PM2.5, PM10, and serum levels of the inflammatory marker, C-reactive protein, already available in 7,566 CA MEC participants. In each of these aims, we will also assess the extent to which these PM-associations are modified by co-pollutants (e.g., NO2 and NOx traffic markers), individual-level (e.g., race/ethnicity, gender, smoking status), and neighborhood-level (e.g., socioeconomic status, ethnic enclave) factors. The strengths of this proposal include: (1) it represents one of the first prospective air pollution and lung cancer and COPD study to include sizeable numbers of Africans and Latinos (n=80,489); (2) it addresses the complexity of air pollution assessment by evaluating three separate measures of estimated air pollutants having different advantages and functionalities; (3) it leverages multiple measures of exposures over the same periods to provide a greater depth in understanding exposure patterns and associations with risk; and (4) it incorporates a molecular epidemiology component. Through this work, we expect to increase our understanding of the burdens of lung cancer and COPD associated with air pollution exposure and to identify differences in associations among important subgroups.